The invention relates to a recombination device, as well as a method for recombining hydrogen and/or carbon monoxide with oxygen, for which at least one catalyst system is arranged inside a housing through which the gaseous mixture can flow during the operational phase, in particular a nuclear power plant.
The simultaneously filed German Application with File Number 199 14 823.6, entitled “KATALYTISCHES ELEMENT ZUR REKOMBINATION VON WASSERSTOFF UND/ODER KOHLENMONOXID MIT SAUERSTOFF” [Catalytic Element for the Recombination of Hydrogen and/or Carbon Monoxide with Oxygen] deals with a similar topic, the disclosure content of which must be included in this application.
Following an accident with cooling agent loss, large amounts of hydrogen and carbon monoxide can be released into a safety container (containment) of a nuclear power plant. Without counter measures, the hydrogen in the atmosphere of the containment can be enriched to such a degree that an explosive mixture can form. With a later accidental ignition, the integrity of the containment can be endangered, particularly if larger amounts of hydrogen burn up.
Different devices are under discussion for preventing explosive gaseous mixtures of this type inside the containment. These devices include, for example, catalytic recombination devices, catalytically and electrically operated ignition devices or a combination of the two above-mentioned devices. The principal mode of operation of catalytic recombination devices is known, for example, from the field of electrochemical engineering and is explained, e.g. in: “ELEKTROCHEMISCHE VERFAHRENS-TECHNIK” [Electrochemical Engineering], DECHEMA1 Monographs, 1970–1992, Volume 97, pages 363–376, Meeting of the Expert Team for Applied Electrochemistry), Chanie Publishing House. 1 Note: DECHEMA=German Association for Chemical Equipment
An early and flameless recombination of the hydrogen and/or the carbon monoxide with oxygen in particular is the goal to remove the hydrogen and the carbon monoxide from the containment atmosphere. In the process, a significant pressure build-up caused by a virulent hydrogen combustion is to be safely avoided. A suitable, early starting recombination device, which does not essentially decrease in activity even after longer operating times in the containment atmosphere and which starts up passively at low environmental temperatures, is known from German Patent Application DE 196 36 557 A1. A recombination arrangement of this type permits a “soft” recombination of the hydrogen, e.g. during a containment atmosphere phase with steam, which is therefore protected against spontaneous combustion.
A recombination device is disclosed in the EP 0 527 968 B1, which provides for a number of catalyst systems in the form of flat panels that are coated on both sides with a catalyst material such a platinum and/or palladium. This device is particularly suitable for the reduction of hydrogen in the containment atmosphere of a nuclear power plant. Each catalyst system comprises a carrier plate of stainless steel, which is provided on both sides with a thin layer of in particular platinum and/or palladium and has a thickness in the micrometer range. A plurality of such coated individual plates is arranged inside a housing that can be designed as a module. The gaseous flow to be monitored flows from the bottom into the housing and leaves the housing in the upper region through an exit opening on the side.
A recombination system with a protective housing is known from EP 0 436 942 A1, which opens up automatically in dependence on an outer temperature. However, the protective housing is closed in the operating phase of the recombination system, so as to avoid contamination of the catalytically active surface of the recombination device.
A recombination device disclosed in EP 0 416 140 A1, on the other hand, is provided with filtering means for retaining pollutants from the atmosphere, e.g. aerosols, thus protecting the catalyst of the recombination device against contamination.
Precious metal alloys are furthermore known from German Patent Application DE 37 25 290, which absorb or discharge the reaction heat developing during the recombination by means of a carrier plate or a metal mesh to prevent an ignition of the gaseous mixture.
A recombination device is known from EP 0 388 955 A1, which is additionally provided with an ignition device for triggering a controlled hydrogen combustion.
Each known recombination system is designed for a particularly high recombination device capacity with particularly low component dimensions, as well as for high resistance to pollutants. When using a recombination device for recombining hydrogen in a gaseous mixture in a nuclear power plant, it must also be ensured that no influences that negatively effect the safety of the nuclear power plant can occur. It should furthermore be taken into account that the catalyst system of a recombination device used for the recombination of hydrogen generally heats up as a result of the recombination. As a result, it could contribute unintentionally to the ignition of the gaseous mixture inside the containment atmosphere of the nuclear power plant because of its increased temperature.